Wideband antenna

ABSTRACT

A monoconical antenna comprises: a substantially conical concavity formed in one end face of a dielectric; a radiation electrode provided on the surface of the concavity; and a ground conductor provided in proximity to and substantially in parallel with the other end face opposite the one end face of the dielectric. The monoconical antenna is so constituted that electrical signals are fed to between the near vertex region of the radiation electrode and the region of the ground conductor. The half-cone angle α of the substantially conical concavity formed in the one end face of the dielectric is determined by a predetermined rule corresponding to relative dielectric constant ε r . Thus, the quality of wideband characteristics inherent in the monoconical antenna can be sufficiently maintained, and further size reduction can be accomplished by dielectric loading.

TECHNICAL FIELD

The present invention relates to an antenna used in radio communicationincluding wireless LAN. More particularly, it relates to a widebandantenna comprising a radiation electrode provided in a substantiallyconical concavity formed in one end face of a dielectric; and a groundconductor provided on the other end face of the dielectric.

Further particularly, the present invention relates to a widebandantenna wherein its inherent quality of wideband characteristics issufficiently maintained and further size reduction is accomplished bydielectric loading. Especially, it relates to a wideband antenna whereinreduction in profile and width is accomplished regardless of theselection of dielectric.

Further, the present invention relates to a wideband antenna whose bandis widened using resistive loading on a radiation conductor, and to awideband antenna comprising a radiation conductor which can bemass-produced with ease and is constituted by resistive loading.

BACKGROUND ART

With the enhancement of speed of and the reduction in the price ofwireless LAN systems, recently, the demand for them has significantlygrown. Especially these days, the introduction of personal area network(PAN) has been widely considered to build a small-scale wireless networkamong a plurality of pieces of electronic equipment common around thehouse for information communication. For example, different radiocommunication systems have been defined using frequency bands, such as2.4-GHz band and 5-GHz band, for which licenses from competentauthorities are unnecessary.

In radio communication including wireless LAN, information istransmitted through antennas. For example, a monoconical antennacomprises a radiation electrode formed in a substantially conicalconcavity in a dielectric, and a ground electrode formed on the bottomface of the dielectric. Thus, a small antenna having relatively widebandcharacteristics can be constituted by the wavelength shortening effectfrom the dielectric positioned between the radiation electrode and theground electrode.

An antenna having wideband characteristics can be used in UWB(Ultra-WideBand) communication wherein, for example, data is spread inas ultra-wide a frequency band as 3 GHz to 10 GHz for transmission andreception. A small antenna contributes to reduction in the size andweight of radio equipment.

For example, Japanese Unexamined Patent Publication No. Hei8(1996)-139515 discloses a small dielectric vertical polarizationantenna for wireless LAN. This dielectric vertical polarization antennais constituted as follows: one base of a cylindrical dielectric isconically hollowed out, and a radiation electrode is formed there, andan earth electrode is formed on the base on the opposite side. Theradiation electrode is drawn out to the earth electrode side through aconductor in a through hole. (Refer to FIG. 1 in the Unexamined PatentPublication.)

FIG. 5 in the Unexamined Patent Publication illustrates the antennacharacteristics of this dielectric vertical polarization antenna.According to the figure, its operating band is approximately 100 MHz.(The center frequency is approximately 2.5 GHz; therefore, the relativebandwidth is approximately 4%.) The monoconical antenna has inherentlyan operating band not less than one octave; therefore, it cannot be saidthat the above antenna sufficiently delivers expected widebandcharacteristics.

The miniaturization of an antenna means reduction in, for example, itsprofile or width. For example, Japanese Unexamined Patent PublicationNo. Hei 9(1997)-153727 presents a proposal with respect to reduction inthe width of monoconical antenna. However, the proposal is such that aradiation conductor should be simply formed in the shape ofsemi-elliptic solid of revolution, and whether it is applicable to thestructure of an antenna whose side face is covered with dielectricwithout any modification is unknown.

FIG. 31 schematically illustrates the constitution of a monoconicalantenna having a single conical radiation electrode. The monoconicalantenna illustrated in the figure comprises a radiation conductor formedin substantially conical shape, and a ground conductor formed with a gapprovided between it and the radiation conductor. Electrical signals arefed to the gap.

FIG. 32 illustrates an example of the VSWR (Voltage Standing Wave Ratio)characteristics of a monoconical antenna. A VSWR not more than 2 isattained over a wide range from 4 GHz to 9 GHz, and this indicates thatthe antenna has a wide relative bandwidth.

One of known methods for further widening the band of this monoconicalantenna is loading resistance on the radiation conductor. FIG. 33 andFIG. 34 illustrate examples of the constitutions of monoconical antennaswhose radiation conductor is formed of a low-conductivity membercontaining a resistance component, instead of high-conductivity metal.With this constitution, reflective power to a feeding portion isdiminished, and this results in expanded matching band. Especially,since the lower limit frequency of the matching band is expanded(downward), the above constitutions are also utilized as means for thereduction of antenna size. As illustrated in FIG. 33, the radiationelectrode may be formed of a material having a constant lowconductivity. However, if the conductivity is distributed as illustratedin FIG. 34 (lower conductivity on the upper base side), the effect isproduced better.

Various methods are known for loading resistance on the radiationconductor of a monoconical antenna. Concrete examples include a methodof sticking a low-conductivity member formed in sheet shape to a conicalinsulator, and a method of applying a low-conductivity member preparedas coating material. (Refer to “Optimization of a Conical Antenna forPulse Radiation: An Efficient Design Using Resistive Loading,” writtenby James G. Maloney, et al. (IEEE Transactions on Antennas andPropagation, Vol. 41, No. 7, July, 1993, pp. 940-947), for example.)

However, if mass production is considered, the method of sticking asheet is indeed inferior in productivity, and is not realistic. With themethod of applying coating, it is difficult to make the thickness ofcoating uniform to control conductivity, and this method is alsounrealistic.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide an excellentmonoconical antenna comprising a radiation electrode provided in asubstantially conical concavity formed in one end face of a dielectric,and a ground conductor provided on the other end face of the dielectric.

Another object of the present invention to provide an excellentmonoconical antenna wherein its inherent quality of widebandcharacteristics is sufficiently maintained and further size reduction isaccomplished by dielectric loading.

A further object of the present invention is to provide an excellentmonoconical antenna wherein reduction in profile and width isaccomplished regardless of the selection of dielectric.

A further object of the present invention is to provide an excellentmonoconical antenna having a feeding portion structure suitable for massproduction.

A further object of the present invention is to provide an excellentconical antenna wherein resistance is loaded on its radiation conductorfor band widening.

A further object of the present invention is to provide an excellentantenna comprising a radiation conductor which can be mass-produced withease and is constituted by resistive loading.

The present invention has been made with the above problems taken intoaccount. A first aspect of the present invention is a monoconicalantenna comprising: a substantially conical concavity formed in one endface of a dielectric; a radiation electrode provided on the surface ofthe concavity; and a ground conductor provided in proximity to andsubstantially in parallel with the other end face of the dielectricopposite the one end face. The monoconical antenna is so constitutedthat electrical signals are fed to the part between the near vertexregion of the radiation electrode and the region of the groundconductor.

The monoconical antenna is characterized in that:

-   -   the half-cone angle α of the substantially conical concavity        formed in the one end face of the dielectric is determined by a        predetermined rule according to relative dielectric constant        ε_(r).

However, “half-cone angle of concavity” herein referred to is defined asthe angle formed between the central axis of a cone and its side face.

According to the present invention, the quality of widebandcharacteristics a monoconical antenna inherently has is sufficientlymaintained and further size reduction is accomplished by dielectricloading.

The half-cone angle α of the substantially conical concavity formed inthe one end face of the dielectric can be determined by the followingexpression that describes its relation with relative dielectric constantε_(r):α=0.8·tan⁻¹(1.7/ε_(r))+13 (Unit of angle: degree)

From the result of several simulations, the present inventors foundthat: the half-cone angle value which optimizes the matching of acircular cone formed in one end face of a dielectric depends on therelative dielectric constant ε_(r) of the dielectric covered. The aboveapproximate expression is obtained by appropriately formulating anapproximate expression and adjusting its coefficients.

The half-cone angle α of the substantially conical concavity is definedcase by case as follows: in case of a circular cone, the angle is thatformed between the central axis of the circular cone and its side face.In case of an elliptic cone or a pyramid, the angle is the average ofthe minimum angle and the maximum angle formed between the central axisand the side face.

The radiation electrode may be formed so that the substantially conicalconcavity is filled with it.

A second aspect of the present invention is a monoconical antennacomprising: a substantially conical concavity formed in one end face ofa dielectric; a radiation electrode provided on the surface of theconcavity or a radiation electrode provided so that the concavity isfilled with it; and a ground conductor provided in proximity to andsubstantially in parallel with the other end face of the dielectricopposite the one end face. The monoconical antenna is so constitutedthat electrical signals are fed to the part between the near vertexregion of the radiation electrode and the region of the groundconductor.

The monoconical antenna is characterized in that: the ratio of theheight h of the concavity to the effective radius r of the base of theconcavity is determined by a predetermined rule according to therelative dielectric constant ε_(r) of the dielectric.

However, “height of concavity” herein referred to is defined as thelength of the segment of a perpendicular drawn from the vertex of theconcavity to the base of the concavity. “effective radius of base ofconcavity” is defined as the average distance between the center point,for which the point of intersection of the base of the concavity and theperpendicular is taken, and the outer envelope of the base. “Half-coneangle of concavity” is defined as the angle formed between a tangent ofthe side face of the concavity and the perpendicular.

The present inventors found that a setting of the half-cone angle of amonoconical antenna has great influence on impedance matching band.Then, the present inventors derived the following: the impedancematching band can be maximized by determining the half-cone angle α(angle formed between the central axis and the side face of a cone) of aconical concavity formed in one end face of a dielectric by thefollowing expression which describes its relation with relativedielectric constant ε_(r):α=0.8·tan⁻¹(1.7/ε_(r))+13 (Unit of angle: degree)

That is, the optimum half-cone angle of a circular cone depends on therelative dielectric constant of the dielectric. In a monoconical antennaconstituted based on the above expression, its side face is covered witha dielectric; therefore, the effect of miniaturization is inevitablyproduced. (This is caused by that the wavelength of the electromagneticfield produced between the radiation electrode and the ground conductoris shortened.) In packaging, therefore, a relative dielectric constant,that is, a dielectric is appropriately selected to meet requests forminiaturization, and then a half-cone angle of the circular cone isdetermined.

If a monoconical antenna is formed based only on such a constitutingmethod, reduction in the size of the antenna can be accomplished byenhancing the relative dielectric constant ε_(r) of the dielectric.However, in conjunction with this, the half-cone angle α is also reduced(that is, the antenna becomes longer than is wide). Therefore, theheight of the antenna is not extremely reduced. If it is desired that anantenna is extremely slenderly formed, the relative dielectric constantε_(r) can be enhanced according to the above expression. As a matter offact, however, dielectrics of various relative dielectric constants donot infinitely exist.

In short, the half-cone angle of a circular cone whose profile or widthis reduced deviates from an optimum value which brings favorableimpedance matching. To cope with this, the present invention is soconstituted that it is compensated by stepping the half-cone angle.

A case where low-profile constitution is adopted will be taken as anexample. In this case, the half-cone angle of the concavity is variedstepwise so that it is reduced as it goes from the base portion to thevertex portion in accordance with the following expression. Thisexpression describes the relation between the ratio of the height h ofthe concavity to the effective radius r of the base of the concavity andrelative dielectric constant ε_(r):tan⁻¹(r/h)>0.8·tan⁻¹(1.7/ε_(r))+13 (Unit of angle: degree)

A case where slender constitution is adopted will also be taken asanother example. In this case, the half-cone angle of the concavity isvaried stepwise so that it is increased as it goes from the base portionto the vertex portion in accordance with the following expression. Thisexpression describes the relation between the ratio of the height h ofthe concavity to the effective radius r of the base of the concavity andrelative dielectric constant ε_(r).tan⁻¹(r/h)<0.8·tan⁻¹(1.7/ε_(r))+13 (Unit of angle: degree)

In either case of low-profile constitution and slender constitution, twosteps of half-cone angle are basically sufficient. Needles to add, thenumber of steps maybe increased to three or more, or a portion where thehalf-cone angle is continuously varied may be present.

However, the half-cone angle at the vertex portion of a radiationelectrode must be less than 90 degrees. Further, it is preferable thatvariation in half-cone angle should be gentle in proximity to the vertexportion of a radiation electrode. It follows that an effort should bemade to maintain an equiangular circular cone in proximity to the vertexportion, that is, the feeding portion in accordance with Rumsey'sEquiangular Theory. (For Rumsey's Equiangular Theory, refer to“Frequency Independent Antenna,” written by V. Rumsey (Academic Press,1966)). Care must be taken not to depart from the above principle.Otherwise, the ultra-wideband characteristics inherent in themonoconical antenna can be lost.

Here, the following constitution may be adopted: an electrode forfeeding is formed over the above other end face, and the dielectric ispenetrated. Thus, the radiation electrode and one end of the feedingelectrode are electrically connected together in the near vertex region.Further, the other end of the feeding electrode may be formed so that itreaches the side face of the dielectric. In this case, electricalsignals are fed to between the other end of the feeding electrode andthe ground conductor. Therefore, a feeding portion structure suitablefor mass production is obtained.

A third aspect of the present invention is a monoconical antennacomprising: a substantially conical radiation electrode; and a groundconductor provided in proximity to the radiation electrode. Themonoconical antenna is so constituted that electrical signals are fed tobetween the near vertex region of the radiation electrode and the regionof the ground conductor.

The monoconical antenna is characterized in that:

-   -   the straight line connecting the vertex of the substantially        conical radiation electrode and the center of the base of the        cone is not perpendicular to the base of the cone. However,        “base of cone” herein referred to includes cases where the base        of a cone faces upward.

The monoconical antenna according to the second aspect of the presentinvention is so constituted that: when the antenna is reduced in profileor width based on the optimum value of half-cone angle, deviation of thehalf-cone angle from the optimum value is compensated by stepping thehalf-cone angle. In this case, a problem arises. The half-cone angleobtained when the profile is reduced deviates from the optimum valuewhich brings favorable impedance matching.

To cope with this, the monoconical antenna according to the third aspectof the present invention is so constituted that impedance matching iscompensated by setting the vertex of the circular cone off the center.

A fourth aspect of the present invention is a conical antennacomprising:

-   -   an insulator;    -   a substantially conical concavity formed in one end face of the        insulator;    -   a radiation electrode formed on the internal surface of the        concavity;    -   a stripped portion obtained by circumferentially stripping part        of the radiation electrode;    -   a low-conductivity member filled in the concavity to the level        at which at least the stripped portion is buried; and    -   a ground conductor provided in proximity to and substantially in        parallel with the other end face of the insulator or formed        directly on the other end face of the insulator.

The conical antenna according to the fourth aspect of the presentinvention basically functions as a monoconical antenna. By the way, noconductor is present on the upper base; however, this does not become acause of preventing the proper operation of the monoconical antenna. Inaddition, since the low-conductivity member exists between the twodivided radiation electrodes, the electrical effect equivalent toresistive loading is produced.

The radiation electrode may be formed on the internal surface of theconcavity by plating or the like.

The low-conductivity member may be constituted using rubber or elastomercontaining conductor.

Electrical signals are fed to the gap between the radiation electrodeand the ground conductor. Alternatively, electrical signals may be fedby making a hole in the ground conductor and drawing the vertex regionof the radiation electrode to the back face.

As mentioned above, the presence of the low-conductivity member betweenthe radiation electrodes divided by the stripped portion produces theelectrical effect equivalent to resistive loading. For this purpose, twoor more circumferential stripped portions may be provided as required.

If two or more stripped portions for circumferentially stripping part ofthe radiation electrode are provided, the low-conductivity member filledin the concavity may be provided with multilayer structure. Themultilayer structure is such that members different in conductivity arefilled in the concavity level by level at which each stripped portion isburied. At this time, the low-conductivity members are so distributedthat the conductivity is lower on the base side of the concavity. Thus,the effect of diminishing reflective power to the feeding portion isenhanced, and this results in expanded matching band.

A fifth aspect of the present invention is a conical antenna comprising:

-   -   an insulator;    -   a first substantially conical concavity provided in one end face        of the insulator;    -   a first radiation electrode formed on the internal surface of        the first concavity;    -   a first stripped portion obtained by circumferentially stripping        part of the first radiation electrode;    -   a first low-conductivity member filled in the concavity to the        level at which at least the first stripped portion is buried;    -   a second substantially conical concavity provided in the other        end face of the insulator;    -   a second radiation electrode formed on the internal surface of        the second concavity;    -   a second stripped portion obtained by circumferentially        stripping part of the second radiation electrode; and    -   a second low-conductivity member filled in the concavity to the        level at which at least the second stripped portion is buried.

In the conical antenna according to the fifth aspect of the presentinvention, the formation of the ground conductor on the other end faceof the insulator is omitted. The conical antenna functions as abiconical antenna wherein a radiation electrode is disposed on theinternal surface of each of the substantially conical concavitiessymmetrically formed in both the end faces.

In the biconical antenna according to the fifth aspect of the presentinvention, electrical signals are fed to the gap between the first andsecond radiation electrodes. For this purpose, various methods can beused. For example, parallel lines can be extended from the insulatorside face and connected to the vertex portions of both the radiationelectrodes.

As mentioned above, the presence of the low-conductivity member betweenthe radiation electrodes divided by the stripped portion produces theelectrical effect equivalent to resistive loading. For this purpose, twoor more circumferential stripped portions may be provided in the firstand second radiation electrodes as required.

In this case, the first and second low-conductivity members filled inthe first and second concavities may be respectively provided withmultilayer structure. The multilayer structure is such that membersdifferent in conductivity are filled in the first and second concavitieslevel by level at which each stripped portion is buried. At this time,the low-conductivity members are so distributed that the conductivity islower on the base side of each concavity. Thus, the effect ofdiminishing reflective power to the feeding portion is enhanced, andthis results in expanded matching band.

A sixth aspect of the present invention is a conical antenna comprising:

-   -   an insulator formed in substantially conical shape;    -   a radiation electrode formed on the surface of the substantially        conical insulator;    -   a circumferential slit portion which circumferentially divides        part of the radiation electrode together with the insulator        thereunder;    -   a low-conductivity member filled in the circumferential slit        portion; and    -   a ground conductor provided in proximity to the near vertex        region of the radiation electrode.

In the monoconical antenna according to the sixth aspect of the presentinvention, the low-conductivity member exits between the two dividedradiation electrodes. Therefore, the electrical effect equivalent toresistive loading is produced.

As mentioned above, the presence of the low-conductivity member betweenthe radiation electrodes divided by the slit portion produces theelectrical effect equivalent to resistive loading. For this purpose, twoor more circumferential slit portions may be provided as required.

In this case, low-conductivity members different in conductivity may befilled in the individual circumferential slit portions. At this time,the low-conductivity members are so distributed that the conductivity islower on the base side of the insulator. Thus, the effect of diminishingreflective power to the feeding portion is enhanced, and this results inexpanded matching band.

A seventh aspect of the present invention is a conical antennacomprising:

-   -   a first insulator formed in substantially conical shape;    -   a first radiation electrode formed on the surface of the        substantially conical insulator;    -   a first circumferential slit portion which circumferentially        divides part of the first radiation electrode together with the        insulator thereunder;    -   a first low-conductivity member filled in the first        circumferential slit portion;    -   a second insulator formed in substantially conical shape whose        vertex is opposed to that of the first insulator and whose base        is disposed symmetrically with that of the first insulator;    -   a second radiation electrode formed on the surface of the        substantially conical insulator;    -   a second circumferential slit portion which circumferentially        divides part of the second radiation electrode together with the        insulator thereunder; and    -   a second low-conductivity member filled in the second        circumferential slit portion.

In the conical antenna according to the seventh aspect of the presentinvention, the formation of the ground conductor on the other end faceof the insulator is omitted. The conical antenna functions as abiconical antenna wherein a radiation electrode is disposed on thesurface of each of the substantially conical insulators disposedopposite to each other so that their end faces are symmetrical with eachother.

As mentioned above, the presence of the low-conductivity member betweenthe radiation electrodes divided by the circumferential slit portionproduces the electrical effect equivalent to resistive loading. For thispurpose, two or more circumferential slit portions may be provided asrequired.

In this case, low-conductivity members different in conductivity may befilled in the individual circumferential slit portions which divide thefirst and second radiation electrodes. At this time, thelow-conductivity members are so distributed that the conductivity islower on the base side of the insulator. Thus, the effect of diminishingreflective power to the feeding portion is enhanced, and this results inexpanded matching band.

An eighth aspect of the present invention is a conical antennacomprising:

-   -   an insulator;    -   a substantially conical concavity provided in one end face of        the insulator;    -   a feeding electrode formed on the surface of the near vertex        region in the concavity;    -   a low-conductivity member filled in the concavity; and    -   a ground conductor provided in proximity to and substantially in        parallel with the other end face of the insulator or formed        directly on the other end face of the insulator.

The conical antenna according to the eighth aspect of the presentinvention basically functions as a monoconical antenna, and thelow-conductivity member acts as a radiation conductor.

The feeding electrode may be formed on the surface of the near vertexregion in the concavity by plating or the like. The low-conductivitymember may be constituted using rubber or elastomer containingconductor.

Electrical signals are fed to the gap between the feeding electrode andthe ground conductor. For example, electrical signals are fed by makinga hole in the ground conductor and extending the feeding electrode tothe back face.

The low-conductivity member filled in the concavity may be provided withmultilayer structure wherein members different in conductivity arerespectively filled. At this time, the low-conductivity members are sodistributed that the conductivity is lower on the base side of theconcavity. Thus, the effect of diminishing reflective power to thefeeding portion is enhanced, and this results in expanded matching band.

A ninth aspect of the present invention is a conical antenna comprising:

-   -   an insulator;    -   a first substantially conical concavity provided in one end face        of the insulator;    -   a first feeding electrode formed on the surface of the near        vertex region in the first concavity;    -   a first low-conductivity member filled in the first concavity;    -   a second substantially conical concavity provided in the other        end face of the insulator;    -   a second feeding electrode formed on the surface of the near        vertex region in the second concavity; and    -   a second low-conductivity member filled in the second concavity.

In the conical antenna according to the ninth aspect of the presentinvention, the formation of the ground conductor on the other end faceof the insulator is omitted. The conical antenna functions as abiconical antenna wherein a feeding electrode is disposed on theinternal surface of each of the substantially conical concavitiessymmetrically formed in both the end faces.

In the conical antenna according to the ninth aspect of the presentinvention, electrical signals are fed to the gap between the first andsecond feeding electrodes. For this purpose, various methods can beused. For example, parallel lines can be extended from the insulatorside face and connected to the vertex regions of both the feedingelectrodes.

The first and second feeding electrodes may be formed on the internalsurfaces of the first and second concavities by plating or the like. Thefirst and second low-conductivity members may be constituted of rubberor elastomer containing conductor.

The first and second low-conductivity members filled in the first andsecond concavities may be provided with multilayer structure whereinmembers different in conductivity are respectively filled. At this time,the low-conductivity members are so distributed that the conductivity islower on the base side of the concavities. Thus, the effect ofdiminishing reflective power to the feeding portion is enhanced, andthis results in expanded matching band.

Other objects, features, and advantages of the present invention will beapparent from the following embodiments of the present invention and themore detailed description taken in connection with the accompanyingdrawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a drawing illustrating the appearance and constitution of themonoconical antenna 1 according to a first embodiment of the presentinvention.

FIG. 2 is a drawing illustrating an example of computation (result ofelectromagnetic field simulation) of the frequency characteristics ofthe monoconical antenna based on the constitution according to the firstembodiment of the present invention.

FIG. 3 is a drawing illustrating another example of computation (resultof electromagnetic field simulation) of the frequency characteristics ofthe monoconical antenna based on the constitution according to the firstembodiment of the present invention.

FIG. 4 is a drawing including charts and graphs illustrating half-coneangle versus frequency characteristics (right) and a graph plotted by anexpression for setting half-cone angle according to the presentinvention (left). The figure illustrates the relation between them whenthe relative dielectric constant ε_(r) of the dielectric 10 is 1.

FIG. 5 is another drawing including charts and graphs illustratinghalf-cone angle versus frequency characteristics (right) and a graphplotted by the expression for setting half-cone angle according to thepresent invention (left). The figure illustrates the relation betweenthem when the relative dielectric constant ε_(r) of the dielectric 10 is3.

FIG. 6 is a further drawing including charts and graphs illustratinghalf-cone angle versus frequency characteristics (right) and a graphplotted by the expression for setting half-cone angle according to thepresent invention (left). The figure illustrates the relation betweenthem when the relative dielectric constant ε_(r) of the dielectric 10 is5.

FIG. 7 is a further drawing including charts and graphs illustratinghalf-cone angle versus frequency characteristics (right) and a graphplotted by the expression for setting half-cone angle according to thepresent invention (left). The figure illustrates the relation betweenthem when the relative dielectric constant ε_(r) of the dielectric 10 is8.

FIG. 8 is a drawing illustrating the constitutions of monoconicalantennas so constituted that the half-cone angle α of the substantiallyconical concavity formed in one end face of a dielectric is inaccordance with a predetermined rule corresponding to relativedielectric constant ε_(r).

FIG. 9 is drawings illustrating the antenna characteristics of amonoconical antenna with the optimum half-cone angle for the relativedielectric constant ε_(r) of 2 and 4, respectively.

FIG. 10 is a drawing illustrating an example of a monoconical antennawhose profile is reduced as compared with the optimum half-cone angleconstitution.

FIG. 11 is a drawing illustrating the VSWR characteristics of amonoconical antenna having the constitution illustrated in FIG. 10.

FIG. 12 is a drawing illustrating an example of a monoconical antennawhose width is reduced as compared with the optimum half-cone angleconstitution according to the present invention.

FIG. 13 is a drawing illustrating the VSWR characteristics of amonoconical antenna having the constitution illustrated in FIG. 12.

FIG. 14 is a drawing illustrating an example of the constitution of amonoconical antenna provided with a feeding portion structure suitablefor mass production according to the present invention.

FIG. 15 is a drawing illustrating how a monoconical antenna having theconstitution illustrated in FIG. 14 is mounted on a circuit board.

FIG. 16 is a drawing illustrating the cross-sectional structure of amonoconical antenna using low-profile constitution.

FIG. 17 is the impedance characteristic diagram and VSWR characteristicdiagram of the low-profile monoconical antenna illustrated in FIG. 16.

FIG. 18 is a drawing illustrating the cross-sectional structure of alow-profile monoconical antenna wherein the vertex of the conicalradiation electrode is set off the center by 25% with respect to radius.

FIG. 19 is the impedance characteristic diagram and VSWR characteristicdiagram of the low-profile monoconical antenna illustrated in FIG. 18.

FIG. 20 is a drawing illustrating the constitution of the monoconicalantenna according to a third embodiment of the present invention.

FIG. 21 is a drawing illustrating an example of computation fordemonstrating the electrical effect of the monoconical antenna accordingto the third embodiment of the present invention.

FIG. 22 is drawings illustrating the constitutions of antennas whereintwo electrode stripped portions are formed in the direction of the depthof the concavity formed in an insulator.

FIG. 23 is drawings illustrating examples wherein the formation of theground conductor on the other end face of the insulator. In theseexamples, resistive loading according to the present invention isapplied to biconical antennas constituted by disposing radiationelectrodes on the internal surfaces of substantially conical concavitiessymmetrically formed in both the end faces.

FIG. 24 is a drawing illustrating the cross-sectional structure of anantenna according to another embodiment of the present invention.

FIG. 25 is a drawing illustrating the constitution of a conical antennawherein two stripped and cut portions are formed in the direction of thedepth of the substantially conical radiation electrode formed on aninsulator.

FIG. 26 is a drawing illustrating examples of the constitutions ofbiconical antennas constituted using conical antennas which are formedby providing circumferential stripped and cut portions in the radiationelectrodes formed on the surfaces of conical insulators.

FIG. 27 is a drawing illustrating the cross-sectional structure of theconical antenna according to a further embodiment of the presentinvention.

FIG. 28 is a drawing illustrating the cross-sectional structure of amodification to the conical antenna illustrated in FIG. 27.

FIG. 29 is a drawing illustrating the constitution of a biconicalantenna constituted using a conical antenna which is formed by filling alow-conductivity member in the feeding electrode formed on the surfacesof the conical concavities in an insulator.

FIG. 30 is a drawing illustrating the cross-sectional structure of amodification to the conical antenna illustrated in FIG. 29.

FIG. 31 is a drawing illustrating the constitution (conventionalexample) of a monoconical antenna having a single conical radiationelectrode.

FIG. 32 is a drawing illustrating an example (conventional example) ofthe VSWR (Voltage Standing Wave Ratio) characteristics of a monoconicalantenna.

FIG. 33 is a drawing illustrating the constitution (conventionalexample) of a monoconical antenna wherein a radiation conductor isconstituted of a low-conductivity member containing a resistancecomponent in place of high-conductivity metal.

FIG. 34 is a drawing illustrating the constitution (conventionalexample) of a monoconical antenna wherein a radiation conductor isconstituted of a non-uniform low-conductivity member containing aresistance component in place of high-conductivity metal.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring to the drawings, the embodiments of the present invention willbe described in detail below.

FIRST EMBODIMENT

FIG. 1 illustrates the appearance and constitution of the monoconicalantenna 1 according to the first embodiment of the present invention.

As illustrated in the figure, the monoconical antenna 1 comprises: asubstantially conical concavity 11 formed in one end face of adielectric cylinder 10; a radiation electrode 12 provided on the surfaceof the concavity; and a ground conductor 13 which is provided inproximity to and substantially in parallel with the other end faceopposite the one end face of the dielectric 10. The monoconical antenna1 is so constituted that electrical signals are fed to between the nearvertex region 14 of the radiation electrode 12 and the region of theground conductor 13.

With respect to the half-cone angle a (angle between the central axisand the side face of the cone) of the substantially conical concavity 11formed in the one end face of the dielectric 10, the monoconical antenna1 according to this embodiment is constituted as follows: the half-coneangle α is determined by a predetermined rule according to relativedielectric constant ε_(r). The rule is, for example, as follows:

-   -   (1) If the monoconical antenna 1 is covered with a dielectric        with the relative dielectric constant ε_(r)=2, the monoconical        antenna 1 is so constituted that the half-cone angle is        approximately 45 degrees.    -   (2) If the monoconical antenna 1 is covered with a dielectric        with the relative dielectric constant ε_(r)=3, the monoconical        antenna 1 is so constituted that the half-cone angle is        approximately 37 degrees.    -   (3) If the monoconical antenna 1 is covered with a dielectric        with the relative dielectric constant ε_(r)=5, the monoconical        antenna 1 is so constituted that the half-cone angle is        approximately 28 degrees.    -   (4) If the monoconical antenna 1 is covered with a dielectric        with the relative dielectric constant ε_(r)=8, the monoconical        antenna 1 is so constituted that the half-cone angle is        approximately 23 degrees.

The rule on which the abvoe constitution of the monoconical antenna 1 isbased is Expression (1) below. Expression (1) describes the relationbetween the half-cone angle α of the conical concavity 11 formed in oneend face of the dielectric 10 and relative dielectric constant ε_(r).α=0.8·tan⁻¹(1.7/ε_(r))+13 (Unit of angle: degree)   (1)

The effective range of half-cone angle setting is between the valuegiven by Expression (1) above plus several degrees and minus severaldegrees. Any value within this range does not pose a problem inpractical use.

With the above-mentioned constitution of monoconical antenna, thebandwidth of an antenna is dramatically enhanced.

FIG. 2 and FIG. 3 illustrate examples of computations of the frequencycharacteristics of a monoconical antenna according to this embodiment(the results of electromagnetic field simulations). FIG. 2 illustratesthe frequency characteristics in the form of Smith chart (center: 50Ω)and VSWR characteristic diagram which frequency characteristics aremeasured when the relative dielectric constant ε_(r) is 3 and thehalf-cone angle is 40 degrees. FIG. 3 illustrates them measured when therelative dielectric constant ε_(r) is 8 and the half-cone angle is 22degrees.

In either example of constitution, the antenna has spiralcharacteristics in proximity to the center of the Smith chart, andobtains favorable frequency characteristics. It is said that an antennalhas favorable antenna characteristics in the frequency domain in whichVSWR is not more than 2. In either example of constitution, the relativebandwidth with VSWR≦2 accounts for nearly 100%. It is apparent that thebandwidth is dramatically enhanced as compared with examples ofcharacteristics presented in Japanese Unexamined Patent Publication No.Hei 8(1996)-139515.

With respect to the method for constituting the monoconical antennaaccording to this embodiment, the shape of the concavity 11 formed inone end face of the dielectric 10 is not limited to circular cone. Evenif it is formed in the shape of elliptic cone or pyramid, the effect ofthe present invention is equally produced. If pyramidal concavity isused, the definition of its half-cone angle α is as follows: the averageof the minimum angle and the maximum angle among angles formed betweenthe central axis and the side face.”

There is no special limitation on the outside shape of the dielectriccylinder 10 as well. Basically, any shape, including circular cylinderand prism, is acceptable as long as the radiation electrode is coveredwith it. The radiation electrode may be formed by filling it in theconical concavity 11, instead of forming it on the surface of theconcavity 11.

The effective range of the relative dielectric constant ε_(r) of thedielectric 10 is up to 10 or so.

The present inventors carried out electromagnetic field simulations andapproximately derived Expression (1) above, on which a setting of thehalf-cone angle α of the circular cone formed in the one end face of thedielectric is based. From the results of several simulations, thepresent inventors found the following: as illustrated in FIG. 4 to FIG.7, the half-cone angle value which brings optimum matching of thecircular cone formed in one end face of a dielectric depends on therelative dielectric constant ε_(r) of the dielectric covered. Anapproximated curve significant from the viewpoint of design is obtainedby approximately formulating an approximate expression and adjusting itscoefficients. With respect to FIG. 4 to FIG. 7, additional descriptionwill be given below.

FIG. 4 includes charts and graphs illustrating half-cone angle versusfrequency characteristics (right) and a graph plotting the half-coneangle based on the expression for setting according to the presentinvention (left). (The right charts and graphs illustrate three cases:case where the half-cone angle is 58 degrees, case where the half-coneangle is 40 degrees, and case where the half-cone angle is 24 degrees,from above.) The figure illustrates the relation between them when therelative dielectric constant ε_(r) of the dielectric 10 is 1. Thefrequency characteristic diagrams comprise Smith chart and VSWRcharacteristic diagram.

From the frequency characteristic diagrams on the right of the figure,the following is evident: when the half-cone angle is approximately 58degrees, the Smith chart has a spiral in proximity to the center, andthe relative bandwidth with VSWR≦2 is maximized. That is, the followingis evident: the half-cone angle which brings optimum matching is 58degrees, and further that half-cone angle value is very close to theline plotted by the expression for setting half-cone angle according tothe present invention.

FIG. 5 includes charts and graphs illustrating half-cone angle versusfrequency characteristics (right) and a graph plotting the half-coneangle based on the expression for setting according to the presentinvention (left). (The right charts and graphs illustrate three cases:case where the half-cone angle is 58 degrees, case where the half-coneangle is 40 degrees, and case where the half-cone angle is 24 degrees,from above.) The figure illustrates the relation between them when therelative dielectric constant ε_(r) of the dielectric 10 is 3. Thefrequency characteristic diagrams comprise Smith chart and VSWRcharacteristic diagram.

From the frequency characteristic diagrams on the right of the figure,the following is evident: when the half-cone angle is approximately 40degrees, the Smith chart has a spiral in proximity to the center, andthe relative bandwidth with VSWR≦2 is maximized. That is, the followingis evident: the half-cone angle which brings optimum matching is 40degrees, and further that half-cone angle value is very close to theline plotted by the expression for setting half-cone angle according tothis embodiment.

FIG. 6 includes charts and graphs illustrating half-cone angle versusfrequency characteristics (right) and a graph plotting the half-coneangle based on the expression for setting according to the presentinvention (left). (The right charts and graphs illustrate three cases:case where the half-cone angle is 40 degrees, case where the half-coneangle is 26 degrees, and case where the half-cone angle is 15 degrees,from above.) The figure illustrates the relation between them when therelative dielectric constant ε_(r) of the dielectric 10 is 5. Thefrequency characteristic diagrams comprise Smith chart and VSWRcharacteristic diagram.

From the frequency characteristic diagrams on the right of the figure,the following is evident: when the half-cone angle is approximately 26degrees, the Smith chart has a spiral in proximity to the center, andthe relative bandwidth with VSWR≦2 is maximized. That is, the followingis evident: the half-cone angle which brings optimum matching is 26degrees, and further that half-cone angle value is very close to theline plotted by the expression for setting half-cone angle according tothe present invention.

FIG. 7 includes charts and graphs illustrating half-cone angle versusfrequency characteristics (right) and a graph plotting the half-coneangle based on the expression for setting according to the presentinvention (left). (The right charts and graphs illustrate three cases:case where the half-cone angle is 36 degrees, case where the half-coneangle is 22 degrees, and case where the half-cone angle is 10 degrees,from above.) The figure illustrates the relation between them when therelative dielectric constant ε_(r) of the dielectric 10 is 8. Thefrequency characteristic diagrams comprise Smith chart and VSWRcharacteristic diagram.

From the frequency characteristic diagrams on the right of the figure,the following is evident: when the half-cone angle is approximately 22degrees, the Smith chart has a spiral in proximity to the center, andthe relative bandwidth with VSWR≦2 is maximized. That is, the followingis evident: the half-cone angle which brings optimum matching is 22degrees, and further that half-cone angle value is very close to theline plotted by the expression for setting half-cone angle according tothis embodiment.

SECOND EMBODIMENT

The monoconical antenna comprises a substantially conical concavityformed in one end face of a dielectric cylinder; a radiation electrodeprovided on the surface of the concavity (or provided so that theconcavity is filled with it); and a ground conductor provided inproximity to and substantially in parallel with the other end faceopposite the one end face of the dielectric. The monoconical antenna isso constituted that electrical signals are fed to between the nearvertex region of the radiation electrode and the region of the groundconductor. The monoconical antenna can be constituted as a small antennahaving relatively wideband characteristics because of the wavelengthshorting effect from the dielectric positioned between the radiationelectrode and the ground electrode.

The present inventors found that a setting of the half-cone angle of amonoconical antenna has great influence on impedance matching band.Then, the present inventors derived the following: the impedancematching band can be maximized by determining the half-cone angle α(angle formed between the central axis and the side face of a cone) of aconical concavity formed in one end face of a dielectric by thefollowing expression which describes its relation with relativedielectric constant ε_(r):α=0.8·tan⁻¹(1.7/ε_(r))+13 (Unit of angle: degree)   (2)

That is, the optimum half-cone angle of a circular cone depends on therelative dielectric constant of the dielectric. As illustrated in FIG.8, for example, the optimum half-cone angle is 48 degrees when therelative dielectric constant ε_(r) is 2, and 31 degrees when therelative dielectric constant ε_(r) is 4. FIG. 9 illustrates the antennacharacteristics of a monoconical antenna with an optimum half-cone anglefor the relative dielectric constant ε_(r) of 2 and 4, respectively.However, the figure represents the antenna characteristics by VSWRcharacteristics. From FIG. 9, the following is evident: favorableimpedance matching is obtained over an ultra-wide band by designing themonoconical antenna based on Expression (2) above which describes therelation between the relative dielectric constant ε_(r) and the optimumhalf-cone angle α of the concavity.

In the monoconical antenna constituted based on Expression (2) above,its side face is covered with a dielectric; therefore, the effect ofminiaturization is inevitably produced. (This is caused by that thewavelength of the electromagnetic field produced between the radiationelectrode and the ground conductor is shortened.) In packaging,therefore, a relative dielectric constant, that is, a dielectric isappropriately selected to meet requests for miniaturization, and then ahalf-cone angle of the circular cone is determined.

With the constitution of the monoconical antenna based on Expression (2)above, reduction in the size of the antenna can be accomplished byenhancing the relative dielectric constant ε_(r) of the dielectric.However, in conjunction with this, the half-cone angle α is also reduced(that is, the antenna becomes longer than is wide). Therefore, theheight of the antenna is not extremely reduced. As a matter of fact, lowprofile is often requested.

Extremely slender constitution may be conversely desired sometimes. If amonoconical antenna is constituted according to Expression (2) above,this is accomplished by enhancing the relative dielectric constantε_(r). As a matter of fact, however, dielectrics of various relativedielectric constants do not infinitely exist. Further, availabledielectrics are naturally limited in terms of workability in electrodeformation and cutting and heat resistance. Therefore, a desired slenderconstitution is quite likely to be difficult to implement.

The half-cone angle of a circular cone whose profile or width is reduceddeviates from an optimum value which brings favorable impedancematching. To cope with this, this embodiment is so constituted that itis compensated by stepping the half-cone angle.

More specific description will be given. If low-profile constitution isadopted, the half-cone angle is varied stepwise so that it is reduced asit goes from the base portion to the vertex portion. However, the ratioof the height h of the concavity to the effective radius r of the baseof the concavity is set in accordance with the following expressionwhich describes its relation with relative dielectric constant ε_(r).tan⁻¹(r/h)>0.8·tan⁻¹(1.7/ε_(r))+13 (Unit of angle: degree)   (3)

If slender constituion is adopted, the half-cone angle is varied so thatit is increased as it goes from the base portion to the vertex portion.However, the ratio of the height h of the concavity to the effectiveradius r of the base of the concavity is set in accordance with thefollowing expression which describes its relation with relativedielectric constant ε_(r).tan⁻¹(r/h)<0.8·tan⁻¹(1.7/ε_(r))+13 (Unit of angle: degree)   (4)

In either case of low-profile constitution and slender constitution, twosteps of half-cone angle are basically sufficient. Needless to add, thenumber of steps may be increased to three or more, or a portion wherethe half-cone angle is continuously varied may be present. However, thehalf-cone angle at the vertex portion of a radiation electrode must beless than 90 degrees. Further, it is preferable that variation inhalf-cone angle should be gentle in proximity to the vertex portion of aradiation electrode. It follows that an effort should be made tomaintain an equiangular circular cone in proximity to the vertexportion, that is, the feeding portion in accordance with Rumsey'sEquiangular Theory. (For Rumsey's Equiangular Theory, refer to“Frequency Independent Antenna,” written by V. Rumsey (Academic Press,1966)). Care must be taken not to depart from the above principle.Otherwise, the ultra-wideband characteristics inherent in themonoconical antenna can be lost.

FIG. 10 illustrates an example of a monoconical antenna whose profile isreduced as compared with optimum half-cone angle constitution accordingto the present invention. In the example illustrated in the figure, theprofile is lower than in the optimum half-cone angle constitution. Inthis example, a dielectric with a relative dielectric constant ε_(r) of4 is selected; the height h of the circular cone is set to 6 mm; and theradius r of the base of the circular cone is set to 12.6 mm. Thus, as anatural consequence, the relation expressed by Expression (3) aboveholds.

As illustrated in the figure, further, two step constitution is adopted.With this constitution, the half-cone angle is stepped at a midpoint,and the half-cone angle value α₀ on the base side is set to 70 degreeswith the half-cone angle value α₁ on the vertex side set to 45 degrees.Thus, the half-cone angle value on the vertex side is made smaller thanthat on the base side.

FIG. 11 illustrates the result of a simulation conducted with respect tothe VSWR characteristics of a monoconical antenna having theconstitution illustrated in FIG. 10. As illustrated in the figure,favorable impedance matching is generally obtained, and a state in whichthe impedance matching is greatly lost and thus wideband characteristicsare lost is avoided. If the combination of half-cone angle values ismore finely adjusted, more favorable characteristics would be obtained.

FIG. 12 illustrates an example of a monoconical antenna whose width isreduced as compared with optimum half-cone angle constitution accordingto this embodiment. In the example illustrated in the figure, the widthis smaller than the optimum half-cone angle constitution. In thisexample, a dielectric with a relative dielectric constant ε_(r) of 2 isselected; the height h of the circular cone is set to 17.4 mm; and theradius r of the base of the circular cone is set to 9 mm. Thus, as anatural consequence, the relation expressed by Expression (4) aboveholds.

As illustrated in the figure, further, two step constitution is adopted.With this constitution, the half-cone angle is stepped at a midpoint,and the half-cone angle value α₀ on the base side is set to 11 degreeswith the half-cone angle value α₁ on the vertex side is set to 41degrees. Thus, the half-cone angle value on the vertex side is madelarger than that on the base side.

FIG. 13 illustrates the result of a simulation conducted with respect tothe VSWR characteristics of a monoconical antenna having theconstitution illustrated in FIG. 12. As illustrated in the figure,favorable impedance matching is generally obtained.

FIG. 14 illustrates an example of the constitution of a monoconicalantenna provided with a feeding portion structure suitable for massproduction.

In the example illustrated in the figure, a track-like feeding electrodeis provided on the base of a dielectric, and the feeding electrode and aradiation electrode are electrically connected with each other through ahole made in the center of the bottom of the dielectric. As illustratedin the figure, this feeding electrode is so formed that its one endreaches the dielectric side face.

A ground conductor is also formed on the dielectric base. As illustratedin the figure, the ground conductor is so formed that it averts andencircles the feeding electrode. Further, the ground conductor is alsoso formed that it is extended to the dielectric side face.

The feeding electrode and ground conductor illustrated in FIG. 14 can beeasily formed on the surface of a dielectric by plating, for example.Therefore, use of such a monoconical antenna as illustrated in thefigure makes it possible to follow a technique for so-called surfacemounting when the antenna is mounted on a circuit board in massproduction, and thus the manufacturing process is simplified.

As illustrated in FIG. 15, the body of the monoconical antenna can befixed on and electrically connected with a circuit board only bysoldering the electrodes on the dielectric side face to the electrodeson the circuit board from the surface side.

The ground conductor need not necessarily be formed on the base of adielectric, and alternatively, a ground conductor may be formed on thecircuit board on which the body of the antenna is to be mounted. In thiscase, for example, adhesive may be used to fix the body of the antenna.

The monoconical antennas according to this embodiment illustrated inFIG. 10 and FIG. 12 are so constituted that: when an antenna is reducedin profile or width based on the optimum values of half-cone angleobtained by Expressions (3) and (4) above, deviation of its half-coneangle from the optimum values is compensated. This compensation iscarried out by stepping the half-cone angle, and this results infavorable impedance matching.

If the profile of an antenna is reduced, a problem arises. The half-coneangle of the cone deviates from the optimum value which brings favorableimpedance matching. To cope with this, the vertex of the circular coneof the monoconical antenna is set off the center, and impedance matchingis thereby compensated. This is a modification to the present invention.In this case, the straight line connecting the vertex of thesubstantially conical radiation electrode and the center of the base ofthe cone is not perpendicular to the base of the cone.

An example will be taken. FIG. 16 illustrates the cross-sectionalstructure of a monoconical antenna using low-profile constitution. Inthe example illustrated in the figure, the half-cone angle of thecircular cone is 64.5 degrees, which differs from 31 degrees, theoptimum value with ε_(r)=4. As dielectric to be filled in the areabetween the radiation electrode and the ground conductor, a materialwith a relative dielectric constant ε_(r) of 4 is used. FIG. 17 includesthe impedance characteristic diagram and VSWR characteristic diagram ofthe low-profile monoconical antenna illustrated in FIG. 16. As isevident from the figure, the impedance greatly differs from 50 ohm, andthe VSWR characteristics are impaired, especially, in high frequencydomain.

Meanwhile, FIG. 18 illustrates the cross-sectional structure of alow-profile monoconical antenna where in the vertex of the conicalradiation electrode is set off the center by 25% with respect to radius.In this case, as illustrated in the figure, the straight line connectingthe vertex of the substantially conical radiation electrode and the baseof the cone is not perpendicular to the base of the cone.

FIG. 19 includes the impedance characteristic diagram and VSWRcharacteristic diagram of the low-profile monoconical antennaillustrated in FIG. 18. As is evident from the figure, the impedancecharacteristics are close to 50 ohm, and the VSWR characteristics areenhanced as well. Especially, it is important that the lower limitfrequency of the matching band is lowered.

As mentioned above, it is apparent that if the impedance cannot matchedin a monoconical antenna due to profile reduction or the like, settingthe vertex of the cone off the center is effective as a means forenhancing its characteristics.

Such a low-profile structure as illustrated in FIG. 18 is alsoapplicable when the relative dielectric constant ε_(r)=1, that is, it isapplicable to a monoconical antenna wherein no dielectric material ispresent. Further, the low-profile structure is widely applicable to notonly monoconical antennas covered with a dielectric but also ordinaryconical antennas (antennas provided with a substantially conicalradiation electrode and a ground conductor).

With respect to the method for constituting the monoconical antennaaccording to this embodiment, the shape of the concavity formed in oneend face of the dielectric is not limited to circular cone. Even if itis formed in the shape of elliptic cone or pyramid, the effect of thepresent invention is equally produced.

If pyramidal concavity is used, the definition of its half-cone angle αis as follows: the average of the minimum angle and the maximum angleamong angles formed between the central axis and the side face.

There is no special limitation on the outside shape of the dielectriccylinder as well. Basically, any shape, including circular cylinder andprism, is acceptable as long as the radiation electrode is covered withit. The radiation electrode may be formed by filling it in the conicalconcavity 11, instead of forming it on the surface of the concavity.

THIRD EMBODIMENT

FIG. 20 illustrates the constitution of the monoconical antennaaccording to the third embodiment of the present invention. Themonoconical antenna comprises: an insulator; a substantially conicalconcavity provided in one end face of the insulator; a radiationelectrode formed on the internal surface of the concavity; a strippedportion obtained by circumferentially stripping part of the radiationelectrode; a low-conductivity member filled in the concavity to thelevel at which at least the stripped portion is buried; and a groundconductor provided in proximity to and substantially in parallel withthe other end face of the insulator.

First, the substantially conical concavity is provided in the one endface of the insulator. The radiation electrode is formed on the internalsurface of the concavity by plating or the like. Subsequently, part ofthe radiation electrode is circumferentially stripped by cutting or thelike. Then, the low-conductivity member is filled to the level at whichthe stripped portion is buried. For the low-conductivity member, rubberor elastomer containing conductor is suitable. A desired conductivity isobtained with comparative ease by adjusting the conductor content.Further, the ground conductor is provided in proximity to andsubstantially in parallel with the other end face of the insulator.Needless to add, an electrode may be formed as ground conductor directlyon the other end face of the insulator.

As in conventional monoconical antennas, electrical signals are fed tothe gap between the radiation electrode and the ground conductor. Ifelectrical signals are fed from the back face side of the groundconductor, the same constitution as conventional antennas may adopted.That is, a hole is made in the ground conductor, and the vertex regionof the radiation electrode is extended to the back face side.

The antenna illustrated in FIG. 20 basically functions as a monoconicalantenna. By the way, no conductor is present on the upper base of theconcavity; however, this does not become a cause of preventing theproper operation of the monoconical antenna. In addition, since thelow-conductivity member exists between the two divided radiationelectrodes, the electrical effect equivalent to resistive loading isproduced. (FIG. 20 is depicted so that the concavity is formed on theupper side of the insulator. However, there are not the conceptions oftop and bottom because of the structure of conical antenna. In thisspecification, the end face provided with the concavity is designated asupper base for convenience in description. However, that does not limitthe scope of the present invention. (The is the same with thefollowing.))

FIG. 21 illustrates an example of computation for demonstrating theelectrical effect of the monoconical antenna according to thisembodiment. On the left of the figure is a VSWR characteristic diagramobtained when the electrode stripped portion is not formed, and on theright is that obtained when the stripped portion is formed. (The otherconditions are completely identical.) The conditions for the computationwill be briefly described below. As is evident from the figure, theformation of the electrode stripped portion brings the followingadvantages: the band wherein VSWR is not more than 2 is expanded to thelow-frequency band; the matching property is improved; and band wideningof the conical antenna is accomplished.

(1) Radiation electrode portion: it is assumed that a metal with aconductivity of 1×10⁷S/m is used.

-   -   Upper base diameter: 12.6 mm, height: 12.6 mm.

(2) Low-conductivity member: it is assumed that a material with aconductivity of 2 S/m is used.

(3) Insulator: it is assumed that a dielectric with a relativedielectric constant of 4 is used.

In the example of the constitution of conical antenna illustrated inFIG. 20, one circumferential stripped portion is formed in the radiationelectrode formed on the internal surface of the concavity in theinsulator. The subject matter of the present invention does not limitthe number of the circumferential stripped portions to one. Morespecific description will be given. As mentioned above, the presence ofthe low-conductivity member between the radiation electrodes divided bythe stripped portion produces the electrical effect equivalent toresistive loading. For this purpose, two or more circumferentialstripped portions may be provided as required.

FIG. 22 illustrates the constitutions of conical antennas wherein twoelectrode stripped portions are formed in the direction of the depth ofthe concavity formed in an insulator. In this case, the low-conductivitymember in the concavity may be provided with multilayer structure asillustrated on the right side of the figure. The multilayer structure issuch that low-conductivity members different in conductivity are filledlevel by level at which each electrode stripped portion is buried. Atthis time, the low-conductivity members are so distributed that theconductivity is lower on the upper base side. Thus, the effect ofdiminishing reflective power to the feeding portion is enhanced, andthis results in expanded matching band.

The scope of the present invention is not limited to monoconicalantenna, and the present invention is effective as a resistive loadingmethod for biconical antenna. FIG. 23 illustrates examples wherein theformation of the ground conductor on the other end face of theinsulator. In these examples, the resistive loading according to thepresent invention is applied to biconical antennas formed by disposingradiation electrodes on the internal surfaces of substantially conicalconcavities symmetrically formed in both the end faces.

Each of the biconical antennas illustrated in the figure comprises: aninsulator; a first substantially conical concavity formed in one endface of the insulator; a first radiation electrode formed on theinternal surface of the first concavity; a first stripped portionobtained by circumferentially stripping part of the first radiationelectrode; a first low-conductivity member filled in the concavity tothe level at which at least the first stripped portion is buried; asecond substantially conical concavity formed in the other end face ofthe insulator; a second radiation electrode formed on the internalsurface of the second concavity; a second stripped portion obtained bycircumferentially stripping part of the second radiation electrode; anda second low-conductivity member filled in the concavity to the level atwhich at least the second stripped portion is buried.

In the examples illustrated in FIG. 23, electrical signals are fed tothe gap between both the radiation electrodes. For this purpose, variousmethods can be used. For example, parallel lines can be extended fromthe insulator side face and connected to the vertex regions of both theradiation electrodes. (This method is not shown in the figure.)

As described in connection with FIG. 22, the presence of thelow-conductivity member between the radiation electrodes divided by thestripped portion produces the electrical effect equivalent to resistiveloading. If the resistive loading according to the present invention isapplied to a biconical antenna, this constitution can be similarlyadopted. That is, for the above-mentioned purpose, two or morecircumferential stripped portions may be provided in each of the upperand lower radiation electrodes as required. (Refer to the center of FIG.23.)

As illustrated on the right side of FIG. 23, the low-conductivitymembers in the concavities may be provided with multilayer structure.The multilayer structure is such that the low-conductivity membersdifferent in conductivity are respectively filled to the level at whicheach electrode stripped portion is buried. At this time, thelow-conductivity members are so distributed that the conductivity islower on the base side. Thus, the effect of diminishing reflective powerto the feeding portion is enhanced, and this results in expandedmatching band.

FIG. 24 illustrates the cross-sectional structure of a monoconicalantenna which is a modification to the third embodiment of the presentinvention. The monoconical antenna illustrated in the figure comprises:an insulator formed in substantially conical shape; a radiationelectrode formed on the surface of the substantially conical insulator;a circumferential slit portion which circumferentially divides part ofthe radiation electrode together with the insulator thereunder; alow-conductivity member filled in the circumferential slit portion; anda ground conductor provided in proximity to the near vertex region ofthe radiation electrode.

In the example illustrated in FIG. 24, the radiation electrode is firstformed on the surface of the insulator formed in conical shape. Theradiation electrode can be formed by plating or the like. Subsequently,part of the radiation electrode is circumferentially stripped and cuttogether with the insulator thereunder by cutting or the like. The thusobtained stripped and cut portion is filled with the low-conductivitymember. For the low-conductivity member, rubber or elastomer containingconductor is suitable. A desired conductivity is obtained withcomparative ease by adjusting the conductor content. Further, the groundconductor is provided in proximity to the vertex region of the radiationelectrode.

With the constitution of monoconical antenna illustrated in FIG. 24, thepresence of the low-conductivity member between the two dividedradiation electrodes produces the electrical effect equivalent toresistive loading. (This is the same as the foregoing.)

Needless to add, a support for fixing the disposition of the groundconductor and the insulator is separately required though it is notshown in FIG. 24.

In the example of the constitution of a conical antenna illustrated inFIG. 24, the radiation electrode formed on the surface of the insulatoris provided with only one circumferential stripped and cut portion. Thesubject matter of the present invention does not limit the number of thecircumferential stripped and cut portions to one. More specificdescription will be given. As mentioned above, the presence of thelow-conductivity member between the radiation electrodes divided by thestripped portion produces the electrical effect equivalent to resistiveloading. For this purpose, two or more circumferential stripped and cutportions may be provide as required.

FIG. 25 illustrates the constitution of a conical antenna wherein twostripped and cut portions are formed in the direction of the depth ofthe substantially conical radiation electrode formed on an insulator. Inthis case, low-conductivity members different in conductivity may befilled in the individual stripped and cut portions. At this time, thelow-conductivity members are so distributed that the conductivity islower on the base side of the insulator. Thus, the effect of diminishingreflective power to the feeding portion is enhanced, and this results inexpanded matching band.

The scope of the embodiment of the present invention illustrated in FIG.24 is not limited to monoconical antenna, and the embodiment iseffective as a resistive loading method for biconical antenna. FIG. 26illustrates examples of the constitutions of biconical antennas usingconical antennas which are formed by providing circumferential strippedand cut portions in the radiation electrodes formed on the surfaces ofconical insulators.

Biconical antenna illustrated or the left of FIG. 26 comprises a firstinsulator formed in substantially conical shape; a first radiationelectrode formed on the surface of the substantially conical insulator;a first circumferential slit portion which circumferentially dividespart of the first radiation electrode together with the insulatorthereunder; a first low-conductivity member filled in the firstcircumferential slit portion; a second insulator formed in substantiallyconical shape whose vertex is opposed to that of the first insulator andwhose base is symmetrical with that of the first insulator; a secondradiation electrode formed on the surface of the substantially conicalinsulator; a second circumferential slit portion which circumferentiallydivides part of the second radiation electrode together with theinsulator thereunder; and a second low-conductivity member filled in thesecond circumferential slit portion.

As illustrated in FIG. 26, the formation of the ground conductor on theother end face of each insulator in proximity to the near vertex regionof the radiation electrode is omitted. The conical insulators are sodisposed that their respective vertexes are opposed to each other andtheir respective bases are symmetrical with each other, and theradiation electrode is formed on the surface of each conical insulator.Part of each radiation electrode is circumferentially stripped and cuttogether with the insulator thereunder, and these stripped and cutportions are filled with the low-conductivity member. Needless to add, asupport for fixing the disposition of the two conical antennas isrequired though it is not shown in the figure.

In the example illustrated in FIG. 26, electrical signals are fed to thegap between both the radiation electrodes. For this purpose, variousmethods can be used. For example, parallel lines can be extended fromthe insulator side face and connected to the vertex regions of both theradiation electrodes. (This method is not shown in the figure.)

As mentioned above, the present of the low-conductivity member betweenthe radiation electrodes divided by the stripped and cut portionproduces the electrical effect equivalent to resistive loading. If theresistive loading according to the embodiment of the present inventionillustrated in FIG. 24 is applied to a biconical antenna, thisconstitution can be similarly adopted. For this purpose, as described inconnection with FIG. 25, two or more circumferential stripped and cutportions may be provided in each of the upper and lower radiationelectrode as required. (Refer to the right side of FIG. 26.)

As illustrated on the right side of FIG. 26, low-conductivity membersdifferent in conductivity may be filled in the two stripped and cutportions formed in the direction of the depth of the substantiallyconical radiation electrode formed on each of the upper and lowerinsulators. At this time, the low-conductivity members are sodistributed that the conductivity is lower on the upper base side. Thus,the effect of diminishing reflective power to the feeding portion isenhanced, and this results in expanded matching band.

FIG. 27 illustrates the cross-sectional structure of a monoconicalantenna which is another modification to the third embodiment of thepresent invention. The monoconical antenna illustrated in the figurecomprises: an insulator; a substantially conical concavity provided inone end face of the insulator; a feeding electrode formed on the surfaceof the near vertex region in the concavity; a low-conductivity memberfilled in the concavity; and a ground conductor provided in proximity toand substantially in parallel with the other end face of the insulatoror formed directly on the other end face of the insulator.

In the example illustrated in the figure, the conical concavity is firstformed in the surface of the insulator, and then the feeding electrodeis formed on the internal surface of the concavity in proximity to itsvertex. The feeding electrode can be formed by plating or the like.Subsequently, the concavity is filled with the low-conductivity member.For the low-conductivity member, rubber or elastomer containingconductor is suitable. A desired conductivity is obtained withcomparative ease by adjusting the conductor content. Then, the groundconductor is provided in proximity to and substantially in parallel withthe other end face of the insulator. Alternatively, the ground conductormay be formed directly on the other end face of the insulator.

With the constitution of monoconical antenna illustrated in FIG. 27, thelow-conductivity member functions as a radiation conductor, and furtherthe electrical effect equivalent to resistive loading is obtained. Asillustrated in the figure, the area of the electrode is significantlyreduced, and the cost can be accordingly reduced. Unlike theabove-mentioned embodiments, the electrode stripping process is omitted,and the cost can be accordingly reduced.

Electrical signals are fed to the gap between the feeding electrode andthe ground conductor. If electric signals are fed from the back faceside of the ground conductor, such a constitution that a hole is made inthe ground conductor and the vertex region of the concavity is extendedto the back face side may be adopted.

FIG. 28 illustrates a modification to the monoconical antennaillustrated in FIG. 27. As illustrated in FIG. 28, the low-conductivitymember filled in the concavity maybe provided with multilayer structurewherein members different in conductivity are respectively filled toindividual predetermined levels. At this time, the low-conductivitymembers are so distributed that the conductivity is lower on the upperbase side. Thus, the effect of diminishing reflective power to thefeeding portion is enhanced, and this results in expanded matching band.

The scope of the embodiment of the present invention illustrated in FIG.27 is not limited to monoconical antenna, and the embodiment iseffective as a resistive loading method for biconical antenna. FIG. 29illustrates the cross-sectional structure of a biconical antennaconstituted using conical antennas which are formed by filling alow-conductivity member in feeding electrodes formed on the surfaces ofthe conical concavities in an insulator.

In the biconical antenna illustrated in FIG. 29, the formation of theground conductor on both the end faces of the insulator is omitted. Thebiconical antenna comprises: a first conical concavity and a secondconical concavity symmetrically formed in both the end faces; a firstfeeding electrode formed on the surface of the near vertex region in thefirst concavity; a first low-conductivity member filled in the firstconcavity; a second feeding electrode formed on the surface of the nearvertex region in the second concavity; and a second low-conductivitymember filled in the second concavity.

With the constitution of biconical antenna illustrated in FIG. 29, thelow-conductivity members function as radiation conductors, and furtherthe electrical effect equivalent to resistive loading is obtained. Asillustrated in the figure, the area of the electrodes is significantlyreduced, and the cost can be accordingly reduced. Unlike theabove-mentioned embodiments, the electrode stripping process is omitted,and the cost can be accordingly reduced.

In the example illustrated in FIG. 29, electrical signals are fed to thegap between the first and second feeding electrodes. For this purpose,various methods can be used. For example, parallel lines can be extendedfrom the insulator side face and connected to the vertex regions of boththe radiation electrodes. (This method is not shown in the figure.)

FIG. 30 illustrates an modification to the biconical antenna illustratedin FIG. 29. As illustrated in FIG. 30, the low-conductivity memberfilled in each concavity may be provided with multilayer structurewherein members different in conductivity are respectively filled toindividual predetermined levels. At this time, the low-conductivitymembers are so distributed that the conductivity is lower on the upperbase side. Thus, the effect of diminishing reflective power to thefeeding portion is enhanced, and this results in expanded matching band.

In the embodiments mentioned above referring to the figures, theradiation electrode of the conical antenna is formed in conical shape.The subject matter of the present invention is not limited to this, andeven if the shape of the radiation electrode is elliptic cone orpyramid, the effect of the present invention is equally produced. Thereis no special limitation on the outside shape of the insulator cylinder,either and basically, any shape, including circular cylinder and prism,easy to handle may be adopted. Further, the insulator is not limited todielectric, and even a magnetic material does not have influence on theessential effect of the present invention.

Up to this point, the present invention has been described in detailreferring to specific embodiments. However, it is further understood bythose skilled in the art that various changes and modifications may bemade in the embodiments without departing from the spirit and scope ofthe present invention. That is, the present invention has been disclosedin the form of exemplification, and all matter contained therein shallnot be interpreted in a limiting sense. The scope of the presentinvention is therefore to be determined solely by the appended claims.

INDUSTRIAL APPLICABILITY

According to the present invention, an excellent monoconical antennawherein its inherent quality of wideband characteristics is sufficientlymaintained and further size reduction is accomplished by dielectricloading can be provided.

Further, according to the present invention, the scope of application ofa dielectric loading monoconical antenna can be dramatically expandedand thus the antenna can be brought into practical use, for example, asa small antenna for ultra-wide band communication system.

Further, according to the present invention, an excellent monoconicalantenna wherein reduction in profile and width is accomplishedregardless of the selection of dielectric can be provided.

Further, according to the present invention, an excellent monoconicalantenna having a feeding portion structure suitable for mass productioncan be provided.

If the constituting methods according to the present invention are usedwhen a monoconical antenna is reduced in size by dielectric loading, thequality of wideband characteristics inherent in the monoconical antennacan be sufficiently maintained. At the same time, the low-profile orslender constitution can be adopted. The thus obtained antenna isuseful, for example, as a small, low-profile antenna or small, slenderantenna for ultra-wide band communication system.

Further, according to the present invention, an excellent conicalantenna wherein resistance is loaded on its radiation conductor for bandwidening can be obtained.

Further, according to the present invention, an excellent conicalantenna comprising a radiation conductor which can be mass-produced withease and is constituted by resistive loading can be provided.

If the constituting methods according to the present invention are usedwhen a monoconical antenna or biconical antenna is widened in band orreduced in size by resistive loading, the antenna can be mass-producedwith ease. Then, the scope of application of the resistive loadingconical antenna can be expanded to consumer products. For example, theantenna can be brought into practical use as a small antenna forconsumer ultra-wide band communication system.

1. A monoconical antenna which comprises: a substantially conicalconcavity formed in one end face of a dielectric; a radiation electrodeprovided on the surface of said concavity; and a ground conductorprovided in proximity to and substantially in parallel with the otherend face opposite the one end face of said dielectric, and is soconstituted that electrical signals are fed to between the near vertexregion of said radiation electrode and the region of said groundconductor, wherein the half-cone angle α (angle between the central axisand the side face of a cone) of the substantially conical concavityformed in the one end face of said dielectric is determined by apredetermined rule according to relative dielectric constant ε_(r). 2.The monoconical antenna according to claim 1, wherein the half-coneangle α of the substantially conical concavity formed in the one endface of said dielectric is determined by the following expression whichdescribes its relation with relative dielectric constant ε_(r):α=0.8·tan⁻¹(1.7/ε_(r))+13 (Unit of angle: degree)
 3. The monoconicalantenna according to claim 1, wherein the half-cone angle α of saidsubstantially conical concavity is defined as the angle between thecentral axis and the side face for circular cone and as the average ofthe minimum angle and the maximum angle among angles between the centralaxis and the side face for elliptic cone or pyramid.
 4. The monoconicalantenna according to claim 1, wherein the radiation electrode is soformed that said substantially conical concavity is filled therewith. 5.A monoconical antenna which comprises: a substantially conical concavityformed in one end face of a dielectric; a radiation electrode providedon the surface of said concavity or a radiation electrode provided sothat said concavity is filled therewith; and a ground conductor providedin proximity to and substantially in parallel with the other end faceopposite the one end face of said dielectric, and is so constituted thatelectrical signals are fed to between the near vertex region of saidradiation electrode and the region of said ground conductor, wherein theratio of the height h of said concavity to the effective radius r of thebase of said concavity is determined by a predetermined rule accordingto the relative dielectric constant ε_(r) of said dielectric.
 6. Themonoconical antenna according to claim 5, wherein the ratio of theheight h of said concavity to the effective radius r of the base of saidconcavity is determined by the following expression which describes itsrelation with relative dielectric constant ε_(r):tan⁻¹(r/h)>0.8·tan⁻¹(1.7/ε_(r))+13 (Unit of angle: degree)
 7. Themonoconical antenna according to claim 6, wherein the half-cone angle ofsaid concavity is varied stepwise or continuously so that it is reducedas it goes from the base portion to the vertex portion.
 8. Themonoconical antenna according to claim 5, wherein the ratio of theheight h of said concavity to the effective radius r of the base of saidconcavity is determined by the following expression which describes itsrelation with relative dielectric constant ε_(r):tan⁻¹(r/h)<0.8·tan⁻¹(1.7/ε_(r))+13 (Unit of angle: degree)
 9. Themonoconical antenna according to claim 8, wherein the half-cone angle ofsaid concavity is varied stepwise or continuously so that it isincreased as it goes from the base portion to the vertex portion. 10.The monoconical antenna according to claim 8, wherein the half-coneangle of said vertex portion is less than 90 degrees.
 11. Themonoconical antenna according to any of claim 1 to claim 10, wherein anelectrode for feeding is formed on said other end face, wherein one endof the feeding electrode penetrates said dielectric and is electricallyconnected with said radiation electrode at the near vertex region, andwherein the other end of the feeding electrode is so formed that itreaches the side face of said dielectric, and electrical signals are fedto between the other end of the feeding electrode and said groundconductor.
 12. A monoconical antenna which comprises: a substantiallyconical radiation electrode; and a ground conductor provided inproximity to said radiation electrode, and is so constituted thatelectrical signals are fed to between the near vertex region of saidradiation electrode and the region of said ground conductor, wherein thestraight line connecting the vertex of said substantially conicalradiation electrode and the center of the base of the cone is notperpendicular to the base of the cone.
 13. The monoconical antennaaccording to claim 12, wherein a dielectric is filled in between saidradiation electrode and said ground conductor.
 14. A conical antennacomprising: an insulator; a substantially conical concavity provided inone end face of said insulator; a radiation electrode formed on theinternal surface of said concavity; a stripped portion obtained bycircumferentially stripping part of said radiation electrode; alow-conductivity member filled in said concavity to the level at whichat least said stripped portion is buried; and a ground conductorprovided in proximity to and substantially in parallel with the otherend face of said insulator or formed directly on the other end face ofsaid insulator.
 15. The conical antenna according to claim 14, whereinsaid radiation electrode is formed on the internal surface of saidconcavity by plating or the like.
 16. The conical antenna according toclaim 14, wherein said low-conductivity member is formed of rubber orelastomer containing conductor.
 17. The conical antenna according toclaim 14, wherein electrical signals are fed to the gap between saidradiation electrode and said ground conductor.
 18. The conical antennaaccording to claim 14, wherein a hole is made in the ground conductorand the vertex region of the radiation electrode is extended to the backface side for feeding electrical signals.
 19. The conical antennaaccording to claim 14, wherein two or more stripped portions obtained bycircumferentially stripping part of said radiation electrode areprovided.
 20. The conical antenna according to claim 19, wherein saidlow-conductivity member filled in said concavity is of multilayerstructure wherein members different in conductivity are filled in saidconcavity level by level at which each of said stripped portions isburied.
 21. The conical antenna according to claim 20, wherein thelow-conductivity members are so distributed that the conductivity islower on the base side of said concavity.
 22. A conical antennacomprising: an insulator; a first substantially conical concavityprovided in one end face of said insulator; a first radiation electrodeformed on the internal surface of said first concavity; a first strippedportion obtained by circumferentially stripping part of said firstradiation electrode; a first low-conductivity member filled in saidconcavity to the level at which at least said first stripped portion isburied; a second substantially conical concavity provided in the otherend face of said insulator; a second radiation electrode formed on theinternal surface of said second concavity; a second stripped portionobtained by circumferentially stripping part of said second radiationelectrode; and a second low-conductivity member filled in said concavityto the level at which at least said second stripped portion is buried.23. The conical antenna according to claim 22, wherein electricalsignals are fed to the gap between said first and second radiationelectrodes.
 24. The conical antenna according to claim 22, wherein saidfirst and second radiation electrodes are formed on the internalsurfaces of said concavities by plating or the like.
 25. The conicalantenna according to claim 22, wherein said first and secondlow-conductivity members are formed of rubber or elastomer containingconductor.
 26. The conical antenna according to claim 22, wherein two ormore stripped portions obtained by circumferentially stripping part ofsaid first and second radiation electrodes.
 27. The conical antennaaccording to claim 26, wherein said first and second low-conductivitymembers filled in said first and second concavities are of multilayerstructure wherein members different in conductivity are filled in saidfirst and second concavities level by level at which each of saidstripped portions is buried.
 28. The conical antenna according to claim27, wherein the low-conductivity members are so distributed that theconductivity is lower on the base side of each of said concavities. 29.A conical antenna comprising: an insulator formed in substantiallyconical shape; a radiation electrode formed on the surface of saidsubstantially conical insulator; a circumferential slit portion whichcircumferentially divides part of said radiation electrode together withthe insulator thereunder; a low-conductivity member filled in saidcircumferential slit portion; and a ground conductor provided inproximity to the near vertex region of said radiation electrode.
 30. Theconical antenna according to claim 29, wherein said radiation electrodeis formed on the surface of said insulator by plating or the like. 31.The conical antenna according to claim 29, wherein said low-conductivitymember is formed of rubber or elastomer containing conductor.
 32. Theconical antenna according to claim 29, wherein two or morecircumferential slit portions which circumferentially divide saidradiation electrode together with the insulator thereunder are provided.33. The conical antenna according to claim 29, wherein low-conductivitymembers different in conductivity are respectively filled in each ofsaid circumferential slit portions.
 34. The conical antenna according toclaim 33, wherein the low-conductivity members are distributed in thecircumferential slit portions so that the conductivity is lower on thebase side of said concavity.
 35. A conical antenna comprising: a firstinsulator formed in substantially conical shape; a first radiationelectrode formed on the surface of said substantially conical insulator;a first circumferential slit portion which circumferentially dividespart of said first radiation electrode together with the insulatorthereunder; a first low-conductivity member filled in said firstcircumferential slit portion; a second insulator formed in substantiallyconical shape whose vertex is opposed to that of said first insulatorand whose base is symmetrical with that of said first insulator; asecond radiation electrode formed on the surface of said substantiallyconical insulator; a second circumferential slit portion whichcircumferentially divides part of said second radiation electrodetogether with the insulator thereunder; and a second low-conductivitymember filled in said second circumferential slit portion.
 36. Theconical antenna according to claim 35, wherein said first and secondradiation electrodes are formed on the surfaces of said first and secondinsulators by plating or the like.
 37. The conical antenna according toclaim 35, wherein said first and second low-conductivity members areformed of rubber or elastomer containing conductor.
 38. The conicalantenna according to claim 35, wherein two or more circumferential slitportions which circumferentially divide said first and second radiationelectrodes together with the insulators thereunder are respectivelyprovided.
 39. The conical antenna according to claim 38, whereinlow-conductivity members different in conductivity are respectivelyfilled in each of the circumferential slit portions which divide saidfirst and second radiation electrodes.
 40. The conical antenna accordingto claim 39, wherein the low-conductivity members are distributed in therespective circumferential slit portions so that the conductivity islower on the base side of each of said insulators.
 41. A manufacturingmethod for conical antenna comprising the steps of: forming asubstantially conical concavity in one end face of an insulator; forminga radiation electrode on the internal surface of said concavity;circumferentially separating part of said radiation electrode to form astripped portion; and filling a low-conductivity member in saidconcavity to the level at which said stripped portion is buried.
 42. Themanufacturing method for conical antenna according to claim 41, furthercomprising the step of: providing a ground conductor in proximity to andin parallel with the other end face of said insulator or directly on theother end face of said insulator.
 43. A manufacturing method for conicalantenna comprising the steps of: forming a radiation electrode on thesurface of an insulator formed in substantially conical shape;circumferentially stripping and cutting part of said radiation electrodetogether with said insulator thereunder to form a stripped and cutportion; and filling a low-conductivity member in said stripped and cutportion.
 44. The manufacturing method for conical antenna according toclaim 43, further comprising the step of: providing a ground conductorin proximity to the vertex region of said radiation electrode.
 45. Aconical antenna comprising: an insulator; a substantially conicalconcavity provided in one end face of said insulator; a feedingelectrode formed on the surface of the near vertex region in saidconcavity; a low-conductivity member filled in said concavity; and aground conductor provided in proximity to and substantially in parallelwith the other end face of said insulator or formed directly on theother end face of said insulator.
 46. The conical antenna according toclaim 45, wherein said feeding electrode is formed on the surface of thenear vertex region in said concavity by plating or the like.
 47. Theconical antenna according to claim 45, wherein said low-conductivitymember is formed of rubber or elastomer containing conductor.
 48. Theconical antenna according to claim 45, wherein electrical signals arefed to the gap between said feeding electrode and said ground conductor.49. The conical antenna according to claim 45, wherein a hole is made inthe ground conductor and said feeding electrode is extended to the backface side for feeding electrical signals.
 50. The conical antennaaccording to claim 45, wherein said low-conductivity member filled insaid concavity is of multilayer structure wherein members different inconductivity are respectively filled.
 51. The conical antenna accordingto claim 50, wherein the low-conductivity members are so distributedthat the conductivity is lower on the base side of said concavity.
 52. Aconical antenna comprising: an insulator; a first substantially conicalconcavity provided in one end face of said insulator; a first feedingelectrode formed on the surface of the near vertex region in said firstconcavity; a first low-conductivity member filled in said firstconcavity; a second substantially conical concavity provided in theother end face of said insulator; a second feeding electrode formed onthe surface of the near vertex region in said second concavity; and asecond low-conductivity member filled in said second concavity.
 53. Theconical antenna according to claim 52, wherein electrical signals arefed to the gap between said first and second feeding electrodes.
 54. Theconical antenna according to claim 52, wherein said first and secondfeeding electrodes are formed on the internal surfaces of said first andsecond concavities by plating or the like.
 55. The conical antennaaccording to claim 52, wherein said first and second low-conductivitymembers are formed of rubber or elastomer containing conductor.
 56. Theconical antenna according to claim 52, wherein said first and secondlow-conductivity members filled in said first and second concavities areof multilayer structure wherein members different in conductivity arerespectively filled.
 57. The conical antenna according to claim 56,wherein the low-conductivity members are so distributed that theconductivity is lower on the base side of each of said concavities. 58.A manufacturing method for conical antenna comprising the steps of:forming a substantially conical concavity in one end face of aninsulator; forming a feeding electrode on the surface of the near vertexregion in said concavity; and filling a low-conductivity member in saidconcavity.